A fuel cell is a novel electric power production system that directly converts chemical energy generated by the electrochemical reaction between fuel (hydrogen or methanol) and an oxidizing agent (oxygen or air) into electrical energy. The fuel cell has attracted considerable attention as a next-generation energy source by virtue of the high energy efficiency and the low contaminant discharge, i.e., the environmental friendly characteristics.
Based on the kinds of electrolytes used, fuel cells are classified into a phosphoric acid fuel cell, an alkaline fuel cell, a polymer electrolyte fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell. Among them, the proton exchange membrane fuel cell is classified as a proton exchange membrane fuel cell using hydrogen gas as fuel or a direct methanol fuel cell in which liquid-phase methanol, as direct fuel, is supplied to an anode.
The polymer electrolyte fuel cell is in the spotlight as a portable power supply unit, a power supply unit for vehicles, or a power supply unit for home use by virtue of low operating temperature of 100° C. or less, elimination of leakage problems due to the use of a solid electrolyte, rapid starting and response characteristics, and excellent durability. Especially, the direct methanol fuel cell has a simple fuel supply system, and the overall structure of the direct methanol fuel cell is not complicated as compared to other fuel cells. Furthermore, the miniaturization of the direct methanol fuel cell is possible. Consequently, research on the direct methanol fuel cell as a portable fuel cell is in progress.
Generally, a unit cell of the fuel cell is constructed in a structure in which an anode and a cathode are applied to opposite sides of an electrolyte membrane made of a polymer material. A methanol solution, as fuel, is supplied to the anode, and air, including oxygen, is supplied to the cathode. Hydrogen ions and electrons are generated from the anode as the result of the oxidation reaction of the methanol. The hydrogen ions move to the cathode through the polymer electrolyte, and reduction reaction occurs between the hydrogen ions and the oxygen. As the result of the reduction reaction, pure water is produced. By the above-described reactions, the electrons move to the cathode via an external circuit with the result that electric power is produced from the fuel cell. At this time, a large amount of carbon dioxide and an unreacted methanol solution are discharged from the anode. The water, the carbon dioxide, and the unreacted methanol generated during the power production of the fuel cell are discharged and recirculated through an additional water controller system.
FIG. 1 is a typical view of a conventional fuel cell system illustrating flow of materials supplied to and generated from a fuel cell.
Referring to FIG. 1, the fuel cell system 100 includes a fuel cell 110, a water controller system 120, and a heat exchanger 130. When electric power is produced using the fuel cell 110, water and carbon dioxide generated from a cathode 111 are introduced into the water controller system 120, and an unreacted methanol solution is introduced into the water controller system 120 from an anode 112. At this time, the water is condensed and collected in the heat exchanger 130 in the form of vapor, and is then introduced into the water controller system 120. The carbon dioxide is discharged through an outlet port 140 of the water controller system 120. The unreacted methanol solution and the water are recirculated to the fuel cell 110 by a liquid pump 150. However, some of the methanol solution gathered in the water controller system 120 is evaporated, and is then discharged through the outlet port 140, which is provided for eliminating the carbon dioxide gas.
Consequently, it is necessary to provide a method of preventing environmental pollution caused due to the discharge of methanol and supplementing the loss of fuel. For example, Japanese Unexamined Patent Publication No. 4-229958 discloses a water controller system constructed in a structure in which unreacted methanol and carbon dioxide are introduced into the lower part of a liquid separator, and the introduced methanol is condensed by a cooling plate disposed at the upper part of the liquid separator, whereby the condensed methanol is collected. In this conventional structure, however, the cooling plate, which condenses the methanol, is needed. Furthermore, an additional device for maintaining the cooling plate at a predetermined temperature or less is needed, and electric power for operating the additional device is also needed.
Also, Japanese Unexamined Patent Publication No. 20044-186151 discloses a water controller system constructed in a structure in which a liquid absorbing member is mounted in the system, which has a hollow part defined in the middle thereof, one end of a gas discharge pipe is located at the liquid absorbing member, and the other end of the gas discharge pipe, which has a liquid separating membrane mounted therein, is located at the hollow part. In this conventional structure, however, there is a strong possibility that the methanol is discharged through the gas discharge pipe, the end of which is located at the liquid absorbing member. Furthermore, the efficiency of the liquid separating membrane is lowered due to continuous use of the water controller system, and therefore, the liquid separation rate is decreased.